The monitoring circuit of a semiconductor device includes: a boot-up controller configured to generate a boot-up enable signal in response to a power-up signal and a boot-up command signal; a read-period generator configured to output a read-period signal in response to a boot-up read signal; and a monitoring unit configured to output the read-period signal to an external output terminal during activation of the boot-up enable signal to allow the read-period signal to be monitored.